A phenomenon where glass or another article is fogged results from that minute water drops are adhered to the surface of the abovementioned articles (or are condensed thereon), and these minute water drops diffuse light. The fogging results in a remarkable lowering of the capacity of glasses, goggles, optical components of optical lenses, spoiling the appearance of window glass for buildings and mirrors, and restricting the place of use as building materials. Furthermore, if the abovementioned fogging occurs on window glass for vehicles including automobiles, the field of sight is restricted, resulting in a serious problem in view of safety.
As a method for solving such problems, there are some methods for preventing them, one of which is a method for coating a surface-active agent to the surface of articles such as glass (for example, Japanese Patent Publication No. 47926 of 1977), another of which is a method for coating a coating agent, the main component of which is hydrophilic absorption resin, to the surface thereof (for example, Japanese laid-open patent publication No. 220428 of 1994), still another of which is a method for fixing hydrophilic particles (for example, Japanese laid-open patent publication No. 328701 of 1992), and the other of which is a method for roughing the abovementioned surface (for example, Japanese laid-open patent publication No. 91042 of 1986).
However, as regards the surface of an article having a surface-active agent coated on glass or other article surface, the sustainability of anti-fogging property is low, and only a temporary effect can be obtained. Furthermore, there is another problem which is a lowering of clear transparency due to glaring or whitening.
Furthermore, the surface of an article obtained by a method for coating a coating agent, which is mainly composed of hydrophilic/absorption resin, to the surface of the abovementioned glass or article, has still another problem, that is, the wear resistance is low, and its durability is inferior to others.
Furthermore, with a method for fixing hydrophilic particles to the abovementioned glass or the surface of other articles, the obtained surface of the article cannot have a sufficient anti-fogging property, is liable to be stained, and the sustainability of the anti-fogging effect is low. Furthermore, with a method for roughing the surface, although such articles are produced by etching with hydrofluoric acid, there is such a problem where the surface of the obtained article has less anti-fogging effect with respect to breath air or steam.
In view of the abovementioned conventional shortcomings and problems, it is therefore an object of the invention to provide an anti-fogging article which is excellent in durability, wear resistance and sustainability of the anti-fogging effect, and a method for producing the same.
Disclosure of the invention
The invention relates to an anti-fogging article on which a film containing metallic oxide fine particles having a grain diameter from 4 through 300 nm and having a metallic oxide as a matrix is coated, wherein dents and projections having an arithmetic mean roughness (Ra) from 1.5 through 80 nm and a mean interval (Sm) from 4 through 300 nm are formed on the abovementioned film surface.
In the invention, by coating a coating solution, which is composed of metallic oxide fine particles, a hydrolyzable, condensable and polymerizable organometallic compound, a compound containing chlorosilyl group, or hydrolyzable substances thereof, onto the substrate, it is possible to form a film containing dents and projections on the surface of the substrate.
As the abovementioned metallic oxide fine particles, a metallic oxide colloid of a single constituent selected from a group consisting of silicon oxide (silica), aluminium oxide (alumina), zirconium oxide (zirconia), titanium oxide (titania), cerium oxide (ceria), or a metallic oxide fine particle consisting of metallic oxide fine particles, mixtures thereof, and complex metallic oxide of two or more constituents thereof may be used. These are preferably used in a form of solvent diffusion sol (colloid solution). The following are available as a metallic oxide sol; for example, sols dispersed in water, which are available on the market, such as "Snowtex-OL", "Snowtex-O", "Snowtex-OUP", "Snowtex-UP", which are silica sols made by Nissan Chemical Industries, Ltd., "Alumina sol 520 " which is an alumina sol also made by the same company, "NZS-30A" zirconia sol made by the same company, "CS-N", "STS-01", "STS-02" which are titania sols made by Ishihara Industries Co., Ltd., "Needler U-15" which is a ceria sol made by Taki Chemical Co., Ltd., "M-6" titania sol made by the same company, a silica sol dispersed in organic solvent which is also available on the market, such as "IPA-ST" or "XBA-ST" made by Nissan Chemical Industries Ltd., and titania sols dispersed in water-alcohol solvent including a binder, which are also available on the market, such as "ST-KO1" or "ST-K03" made by Ishihara Sangyo Co., Ltd.
It is preferable that the grain size of the abovementioned metallic oxide fine particles is from 4 through 300 nm. If the grain size of metallic oxide fine particles is less than 4 nm, the arithmetic mean roughness (Ra) is liable to become less than 1.5 nm and the mean interval (Sm) of dents and projections on a film of the surface of the substrate is liable to become less than 4 nm, no effective dent and projection to improve the anti-fogging capacity and anti-fogging sustainability can be formed, and it is not preferable. To the contrary, if the grain size of metallic oxide fine particles exceeds 300 nm, the arithmetic mean roughness (Ra) becomes 80 nm or more and the mean interval (Sm) of dents and projections of the abovementioned film exceeds 300 nm, wherein the dents and projections are too large, resulting in spoiling the transparency, and since the fine particles are liable to be deposited in the process of production, it is not favorable.
Chain fine particles are preferable as the abovementioned metallic oxide fine particles. By using chain fine particles, the shape of the surface dents and projections becomes three-dimensionally cubic and convex and concave, wherein it is possible to form surface dents and projections which have a high anti-fogging capacity and anti-fogging sustainability. "Snowtex-OUP" and "Snowtex-UP" which are silica sols made by Nissan Chemical Industries, Ltd. may be available as an example of chain colloids. These have a diameter from 10 through 20 nm and a length from 40 through 300 nm.
A dispersion solvent of the abovementioned metallic oxide fine particles is not specially specified if the metallic oxide fine particles are practically dispersed in stability. However, water, methanol, ethanol, or propanol alone or a combination thereof is preferable. Water is further preferable. Water or low-grade alcohol may be easily mixed with a solution containing the abovementioned metallic oxide fine particles, and it can be simply eliminated by drying when forming a film or a heat treatment after the film is formed. Of them, water is the most preferable in view of the production environment.
A dispersion assisting agent may be added to a solution containing the abovementioned organometallic compound and a compound including a chloroslyl group when adding the abovementioned metallic oxide fine particles to the solution. The dispersion assisting agent is not particularly limited. An additive generally used, for example, an electrolyte such as sodium phosphate, hexameta sodium phosphate, sodium pyrophosphate, aluminium chloride, ferric chloride, various kinds of surface-active agents, various kinds of organic macromolecules, silane coupling agents, titanium coupling agents, etc. may be used. The quantity of addition thereof is usually 0.01 through 5 weight percent with respect to the abovementioned metallic oxide fine particles.
A hydrolyzable, condensable, and polymerizable organometallic compound which is added to a coating solution for forming dents and projections along with the abovementioned metallic oxide fine particles may be basically any kind of compound which is hydrolyzable and polymerizable through dehydration. However, metal alkoxides or metal chelates are preferable.
As a metal alkoxide, for example, methoxide, ethoxide, propoxide, butoxide, etc. of silicon, aluminium, zirconium, titanium, etc. may be preferably used as a single body or mixture, and as a metal chelate, acetylacetonate complex of silicon, aluminium, zirconium, titanium, etc. may be preferably used.
Furthermore, as the abovementioned organometallic compound, alkylsilicate of macromolecular type, for example, "ethylsilicate 40" made by Colcoat Corp., and "MS56" made by Mitsubishi Chemical Ltd., etc. may be used.
As a hydrolyzed substance of the abovementioned metal oxide compound, alkoxysilane hydrolysis solution which is available on the market, such as "HAS-10" made by Colcoat Corp., "Ceramica G-91" or "Ceramica G-92-6" made by Nippan Lab. Corp., and "Atoron NSI-500" made by Nippon Soda Co., Ltd., etc. may be used.
A compound containing chlorosilyl group included in a coating solution for forming a dent and projection film along with the abovementioned metal oxide fine particles is a compound having at least one chlorosilyl group (--SiCl.sub.0 X.sub.3-n, wherein n is 1, 2 or 3, X is hydrogen or alkyl group, alkoxy or acyloxy group, the number of carbon of which is from 1 through 10) in a molecule. Of them, a compound having at least two molecules of chlorine is more preferable, and chlorosilane and a condensed and polymerized substance thereof in which at least two molecules of hydrogen in silane Si.sub.n H.sub.2n+2 (wherein n is an integer from 1 through 5) are displaced for chlorine and the other hydrogen is displaced for the abovementioned alkyl group, alkoxy group, or acyloxy group, is preferable. For example, tetrachlorosilane (silicon tetrachloride SiCl.sub.4), trichlorosilane (SiHCl.sub.3), trichloromonomethylsilane (SiCH.sub.3 Cl.sub.3), dichlorosilane (SiCl.sub.4 Cl.sub.2), and Cl-- (SiCl.sub.2 O).sub.n --SiCl.sub.3 (n is an integer from 1 through 10), etc. may be listed.
A hydrolyzed substance of the abovementioned compound containing chlorosilyl group may be used, and a single body or mixture thereof may be also used. However, the compound containing chlorosilyl group which is most preferable is tetrachlorosilane. The chlorosilyl group is very reactive, and the same is able to form a fine film by self condensation or condensation with the surface of the substrate.
The solvent of a solution including the abovementioned organometaliic compound, or chlorosilyl group contained compound, or their hydrolyzed substances may be of any type which is able to practically dissolve the abovementioned organometallic compounds, chlorosilyl group contained compounds, or their hydrolyzed substances. However, alcohol such as methanol, ethanol, propanol, butanol, etc. is most preferable. The abovementioned metal compound, chlorosilyl group contained compound, and/or their hydrolyzed substances are caused to be contained at a concentration ratio from 1 through 30 percents by weight.
Water is requisite to hydrolyze the abovementioned organometallic compounds. This may be either acidic or neutral. However, in order to accelerate the hydrolysis, it is preferable that water which is acidified with hydrochloric acid, nitric acid, sulphuric acid, acetic acid, citric acid, sulfonic acid, etc. is used.
The quantity of addition of water necessary for the hydrolysis of the abovementioned organometallic compound may be 0.1 through 100 (molar ratio) with respect to the quantity of organometallic compounds. If the water addition quantity is less than 0.1 (molar ratio), the promotion of hydrolysis of organometallic compounds is not sufficient, and if the molar ratio exceeds 100, the solution is liable to be unstable. This is not preferable.
The quantity of addition of acid is not specially specified. However, it is better that the quantity thereof is 0.001 through 20 (molar ratio) with respect to the quantity of organometallic compounds. If the quantity of addition thereof is less than 0.001 (molar ratio), the promotion of hydrolysis of organometallic compounds is not sufficient, which is not preferable. And if the addition exceeds 20 (molar ratio), the acidity of the solution becomes too high. This is not preferable in handling the same. In view of only the hydrolysis, the upper limit of the quantity of addition of acid is 2 (molar ratio) with respect to the quantity of organometallic compound. If the quantity of acid is increased more than this, the degree of promotion of hydrolysis will not change. However, by increasing the quantity of addition of acid more than 2, there is a case where the film strength is remarkably increased and where a film which is able to sufficiently endure practical applications through drying at a low temperature (room temperature to 250.degree. C.).
A preferable composition of a coating solution for which an increase of the film strength can be recognized is such that the concentration of metal oxides is 0.001 percents by weight or more and 3 percents by weight or less, the acid concentration is 0.001 moles per liter or more and 1 mole per liter or less, and the water content is 0.001 percents by weight or more and 10 percents by weight or less. A further preferable composition is such that the concentration of the abovementioned metal oxide is 0.01 percents by weight or more and 0.6 percents by weight or less, the acid concentration is 0.01 moles per liter or more and 0.3 moles per liter or less, and the water content is 0.001 percents by weight or more and 3 percents by weight or less. The acid which is used at this time is preferably nitric acid or hydrochloric acid. Furthermore, it is preferable that acid having a concentration which is lower 0.3 times than the water content is used. That is, when acid in a form of water solution is used, it is preferable that the acid is an acid having a concentration ratio of 23.1% or more. When the acid is used in a form of ethanol solution, it is preferable that the acid concentration in the ethanol solution is 0.15 percents by weight or more if the ethanol solution contains, for example, water content of 0.5 percents by weight.
In a case where the abovementioned chlorosilyl group contained compound is used, it is not a requisite that water or acid is added. Even though no water or acid is added, the hydrolysis is carried out with water contained in the solvent or water in the atmosphere. Furthermore, hydrochloric acid is made free in the solution in line with the hydrolysis, wherein the hydrolysis is further promoted. But, there is no problem if water or acid is additionally supplied.
If the content of the abovementioned metal oxide fine particles in a film is too small, an effect of adding metal oxide fine particles, that is, an anti-fogging property and anti-fogging sustainability is not sufficient. To the contrary, if the content of metal oxide fine particles is too large, the matrix phase of metal oxides resulting from organometallic compounds or chlorosilyl group contained compounds is made non-continuous to cause the dents and projections of film to be weakened, wherein the film is liable to be made weak, and further the anti-fogging property and anti-fogging sustainability obtained are saturated to cause no further practical improvement to occur. Therefore, it is preferable that the content of metal oxide fine particles is 5 percents by weight or more and 80 percents by weight or less when converted to the metal oxides. It is further preferable that the content is 10 percents by weight or more and 70 percents by weight or less and still further preferable that the content thereof is 20 percents by weight or more and 60 percents by weight or less.
The abovementioned metal oxide compound is mixed with the abovementioned organometallic compound, chlorosilyl group contained compound or their hydrolyzed substance along with a solvent. As necessary, water, acid catalyst and dispersion assisting agent is added thereto, and a coating liquid to form dents and projections on a substrate is adjusted. At this time, organometallic compound and chlorosilyl group contained compound may be used independently or may be used as a mixture thereof. A favorable blending ratio of the coating liquid is as shown in Table 1 below;
TABLE 1 ______________________________________ Organometallic compound, or chlorosilyl 100 parts by weight group contained compound or their hydrolyzed substance Metal oxide fine particles 10 to 200 parts by weight Water 0 to 150 parts by weight Acid catalyst 0 to 35 parts by weight Dispersion assisting agent 0.001 to 10 parts by weight Solvent 500 to 30,000 parts by weight ______________________________________
The abovementioned metal compound or chlorosilyl group contained compound is dissolved in a solvent, to which a catalyst and water are added, and hydrolysis is carried out for five minutes to two days at an appointed degree of temperature from 10.degree. C. to the boiling point of the solution, wherein metal oxide fine particles are added to the solution along with a dispersion assisting agent as necessary. In this condition, if necessary, the solution is further hydrolyzed for five minutes to two days at an appointed degree of temperature from 10.degree. C. to the boiling point thereof, whereby a coating liquid for forming dents and projections can be obtained. Furthermore, in a case where a chlorosilyl group contained compound is used, it is not a requisite that a catalyst and water are added thereto. Still furthermore, metal oxide fine particles may be added before the abovementioned hydrolysis process is started. Furthermore, in order to omit the hydrolysis process of organometallic compounds, a solution in which organometallic compounds are hydrolyzed, which is available on the market, may be used. Thereafter, the obtained coating liquid may be diluted by a suitable solvent in compliance with the coating method.
The coating liquid for forming dents and projections is coated on a substrate and dried or heat-treated as necessary, whereby metal oxide dents and projections are formed on the substrate.
As a substrate for the present invention, glass, ceramic, plastic or metal, etc. may be available. In a case where, for example, a plastic substrate, etc. having less hydrophilic property is used on the surface of the abovementioned substrate, the surface is plasma-treated or corona-discharged in advance in order to make it hydrophilic, or is subjected to irradiation of ultraviolet rays having a wavelength from around 200 through 300 nm, in an atmosphere including oxygen, for hydrophilic treatment. Thereafter, it is preferable that the abovementioned coating is performed.
Furthermore, although there is a case where the coating liquid for forming dents and projections is not uniformly coated by being shed according to stained conditions on the substrate, this can be improved by washing the surface of the substrate or improving the quality thereof. As a method of washing or improving the quality, many ways, that is, de-oiling washing by an organic solvent such as alcohol, acetone, hexane, etc., washing with alkali or acid, polishing the surface with a polishing agent, ultrasonic cleaning, irradiation of ultraviolet rays, ozone treatment with ultraviolet rays, plasma treatment, corona discharge treatment, heat treatment, etc. are available.
The abovementioned coating method may depend upon an already known technique, and it is not specially specified. There are many methods which are a method of using a device such as a spin coater, roll coater, spray coater, curtain coater, etc., an immersing method (dip coating method), a flow-coating method, and various kinds of printing methods such as a screen printing, gravure printing, curved printing, etc.
After the coated substrate is dried at the appointed temperature from the room temperature to 150.degree. C. for one minute to two hours, heat treatment is carried out at the appointed temperature from 150.degree. C. to the heat resisting temperature of the substrate for five seconds to five hours as necessary. The heat resisting temperature of the substrate is the temperature which is the upper limit of temperature at which the substrate is able to retain its physical properties, wherein as regards glass substrate, for example, a softening point and transparency losing temperature (usually 600.degree. C. to 700.degree. C.), etc., are included in this category, and as regards plastic substrate, for example, glass transition point, crystalization point, and decomposing point, etc. are included therein.
By the abovementioned drying and heat treatment, tough dents and projections of metal oxides are formed on the surface of a substrate. These dents and projections are formed of a matrix of metal oxide fine particles and metal oxides (resulting from organometallic compounds or chlorosilyl group contained compound), wherein metal oxide fine particles are fixed and adhered to the substrate by a metal oxide matrix, and the surface of the metal oxide fine particles form dents and projections of the film. It is preferable that the thickness of the dent and projection film is from 2 through 300 nm, and it is further preferable that the thickness is from 4 through 100 nm.
If the thickness is thinner than 2 nm, the effect of dents and projections is very low, that is, the anti-fogging property is low and is not preferable. If the thickness is greater than 300 nm, the interference color is recognized to be remarkable and is not preferable. Furthermore, if the thickness is less than 4 nm, the anti-fogging sustainability is liable to be lowered, and if the thickness is greater than 100 nm, the wear resistance is liable to be lowered. Both of them are not preferable. A further preferable thickness of the dent and projection film is from 20 through 100 nm. The thickness of the dent and projection film is defined by the difference between the inside surface of the film and the average line of the outside dents and projections.
Articles, on which dents and projections are thus formed on the surface of substrates, improve the slippage property of water, have a low contact angle with water drops, and have an anti-fogging property. Furthermore, even though the surface thereof is more or less stained, the contact angle is not easily increased to cause the anti-fogging property to be sustained.
Furthermore, if light such as ultraviolet rays, etc. is irradiated on the surface of the anti-fogging article in a case where titanium oxide is used as metal oxide fine particles and matrix, there is a case where the surface stains can be decomposed by a light catalyst action and the anti-fogging property is improved. As regards such articles, the anti-fogging property can be semi-permanently sustained under light such as sunlight, fluorescent lamp, etc.
It is preferable that the dent and projection film according to the invention is formed so as to have an arithmetic mean roughness (Ra) from 1.5 through 80 nm and a mean interval (Sm) of dents and projections from 4 through 300 nm, by adjusting the grain size, grain shape of metal oxide fine particles in the abovementioned coating solution, a mixture ratio and solid content concentration of organometallic compounds, chlorosilyl group contained compound, or their hydrolyzed substances with metal oxide fine particles.
In a case where the abovementioned Ra value is smaller than 1.5 nm or larger than 80 nm, the anti-fogging property and anti-fogging sustainability are low, and it is not preferable. Furthermore, if the abovementioned Sm value is smaller than 4nm or larger than 300 nm, the anti-fogging property and anti-fogging sustainability are low, and it is not preferable. In particular, if the Sm value exceeds 300 nm, the transparency may be spoiled to be not preferable. It is further preferable that the dent and projection film according to the invention has an arithmetic mean roughness (Ra) from 5 through 30 nm and a mean interval (Sm) from 5 through 150 nm with respect to the dents and projections, wherein in this range, the anti-fogging property and especially the anti-fogging sustainability are further preferable. Herein, Ra value and Sm value are defined by a description method regulated in the Japanese Industrial Standards JIS B 0601 (1994), and they can be calculated on the basis of section curves observed and measured by an atomic force microscope (for example, Seiko Electronic Co., Ltd., Type SPI3700) and an electron microscope (for example, Hitachi, Limited, Type H-600).
If a surface-active agent is included in the dent and projection film including the abovementioned metal oxide fine particles, the matrix of which is metal oxide, it is possible to obtain an anti-fogging article, the anti-fogging property and anti-fogging sustainability of which are further improved. As a method of impregnating a surface-active agent in the dent and projection film, a method of adding a surface-active agent to the coating solution for forming the abovementioned dents and projections is simple and preferable. The surface-active agent impregnated in the dent and projection film is caused to slowly move onto the surface of a dent and projection film to cause the interfacial force of water drops, which are dew-condensed, to be lowered, thereby causing the spread resulting from slippage of water drops to be increased and causing the anti-fogging property to be further increased. Furthermore, the surface-active agent will cover stain constituents and take a role of preventing the anti-fogging property from being lowered due to stains.
The surface-active agent impregnated in the dent and projection film is retained in clearances formed by metal oxide fine particles and thin pores of the metal oxide matrix and slowly moves onto the surface, wherein the surface-active agent contributes to improvement of the anti-fogging property and hydrophilicity. Therefore, the anti-fogging property or hydrophilicity of a dent and projection film is further improved than that of the dent and projection film not having any surface-active agent. Furthermore, since high anti-fogging property effected by dents and projections can be retained even though the surface-active agent gradually flows out through use and no further surface-active agent which can move from inside the film onto the surface is left over, a group lowering of the anti-fogging property does not occur.
In the present invention, a negative-ionized surface-active agent is preferable as a surface-active agent used to be contained in the dent and projection film. Since a positive-ionized or ampholytic surface-active agent has such a tendency where the surface-active agent is adsorbed onto the dent and projection film consisting of metal oxides with the hydrophilic portion of positive ions oriented thereto, the hydrophobic portion of the surface-active agent is oriented to the air side. Resultantly, since the hydrophilicity on the surface of articles is liable to be lowered to cause the anti-fogging property to be decreased, positive ionized or ampholytic surface-active agents are not preferable. As regards non-ionized surface-active agents, there are many cases where the molecular weight thereof is large, and they are liable to be fixed in the film. Similarly, the hydropholicity on the surface of articles is lowered to cause the anti-fogging property to be spoiled. Therefore, a non-ionized surface-active agent is not preferable.
Furthermore, a surface-active agent having amine nitrogen or amide bond is liable to be adsorbed onto the dent and projection film composed of metal oxides via nitrogen atoms regardless of ion polarity, wherein the anti-fogging property is also lowered. Therefore, the surface-active agent is not preferable. Accordingly, a surface-active agent not containing any amine nitrogen or amide bond in molecules is preferably used.
As a negative-ionized surface-active agent, sulfosuccinic acid ester salt like dialkyl sodium sulfosuccinate, alkylether sulfate, alkylether phosphate, alkylether carbonate are available, and ester salt sulfate, etc. like sodium dodecylbenzene sulfonate is also available. Of them, dialkyl sodium sulfosuccinate, for example, dibutyl sodium sulfosuccinate, dihexyl sodium sulfosuccinate, or di-2-ethylhexyl sodium sulfosuccinate, etc. has a good anti-fogging preventing property and anti-fogging sustainability and is preferably used. These surface-active agents may be used alone or may be used with two or more kinds thereof mixed.
It is preferable that the quantity of a surface-active agent contained in the dent and projection film according to the invention is from 0.1 to 15 percents by weight with respect to the entire dent and projection constituents containing metal oxide fine particles and using metal oxides as a matrix. If the content of surface-active agent is 0.1 weight percent or less, improvement of the anti-fogging property and hydrophilicity is not sufficient, and addition of the surface-active agent does not have any meaning. It is not preferable. On the other hand, if the content thereof exceeds 15 percents by weight, the film is whitened to cause the appearance to be worsened, and furthermore the film strength will be lowered. It is also not preferable.
The dent and projection film including the abovementioned surface-active agent is dried and heat-treated at a temperature lower than the decomposing temperature of the surface-active agent after the film is produced.
By further adding a phosphate compound to the dent and projection film or the dent and projection film containing a surface-active agent according to the invention, it is possible to obtain an anti-fogging article, the anti-fogging property and anti-fogging sustainability of which are further improved. As a method for causing a phosphate compound to be contained in a dent and projection film, a method for adding a phosphate compound into the abovementioned coating liquid for forming dents and projections is simple and preferable.
As the abovementioned phosphate compound, ester phosphate, phosphoric acid, phosphorus oxide, ester phosphite, phosphorous acid, etc. are listed. One or more of these chemical compounds may be used. It is preferable that the content of the abovementioned phosphate compound includes metal oxide fine particles and is from 0.1 to 15 percents by weight with respect to all the constituents of the dent and projection film, the matrix of which is a metal oxide. If the content of surface-active agent is less than 0.1 weight percent, the anti-fogging property and hydrophilicity are not sufficiently improved. On the other hand, if the content thereof exceeds 15 percents by weight, the film is whitened to cause the appearance to be liable to be worsened, and furthermore the film strength will be lowered. It is also not preferable.
Organosilane or its hydrolyzed substance containing in the molecule at least a functional group which is selected from a group consisting of polyalkylene oxido group, alkyl group, alkenyl group, and aryl group is brought into contact with the dent and projection film (regardless of whether the film includes or does not the abovementioned surface-active agent or phosphate compounds), which contains the abovementioned metal oxide fine particles and has a metal oxide as its matrix, and the same is chemically or physically fixed or adhered to the dents and projections on the surface, whereby it is possible to obtain an anti-fogging article, the anti-fogging sustainability of which is further improved.
Polyethylene oxido group, polypropyrene oxido group, etc. may be mainly used as the abovementioned polyalkyl oxido group. As the abovementioned alkyl group, a chain alkyl group having a carbon atom number from 1 to 10 such as methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group, octyl group, nonyl group, decyl group, etc. etc., and ring alkyl group having a carbon atom number from 3 to 10 such as cyclopentyl group, cyclohexyl group, etc. may be mainly used. As the abovementioned alkenyl group, a group having a carbon atom number from 1 to 10 such as vinyl group, allyl group, butenyl group, propenyl group, hexenyl group, octenyl group, cyclohexenyl group, etc. is mainly used. Phenyl group, tolyl group, xylyl group, etc. may be mainly used as the abovementioned aryl group.
Since these functional groups are nonpolar or has low polarity, stains are less adhered to cause an increase of the contact angle to be suppressed with respect to water drops, that is, it is preferable since the anti-fogging sustainability is improved. In particular, as regards the abovementioned anti-fogging articles which are produced by using organosilane including polyalkylene oxido group, the anti-fogging property is excellent and the anti-fogging sustainability is specially excellent.
Since the abovementioned functional groups is non-reactive or has low reaction property, no chemical combination with stains is produced to cause stains not to be fixed on the surface. Therefore, since stains adhered onto the surface can be simply eliminated by wiping, etc., the anti-fogging property can be simply revived even though the anti-fogging property is gone away due to stains.
It is preferable that the abovementioned organosilane is alkoxysilane or chlorosilane containing alkoxyl group or chloro group in the molecule. Since these functional groups are easily subjected to hydrolysis and organosilane is toughly chemically combined to the surface of dents and projections of metal oxides, it is possible to obtain products, the anti-fogging sustainability of which is further improved. Of the abovementioned organosilane, polyalkylene oxido group, for example, lkoxysilane containing polyethylene oxido group, particularly [alkoxy (polyethylene oxy) alkyl] trialkoxysilane, for example, [methoxy (polyethylene oxy) propyl] [trimethoxysilane] is most preferable.
It is preferable that an anti-fogging article for which the abovementioned organosilane or its hydrolyzed substance is chemically or physically fixed or adhered to the dent and projection surface thereof has a contact angle of 10 degrees or less (with respect to water drops of 0.4 mg). If the contact angle exceeds 10 degrees, that is not preferable since the anti-fogging property and anti-fogging sustainability are lowered.
A method for chemically or physically fixing or adhering the abovementioned organosilane or its hydrolyzed substance to the abovementioned dent and projection surface, any type of method for causing the abovementioned organosilane or its hydrolyzed substance to be chemical or physically brought into contact the abovementioned dent and projection surface may be available. For example, a method for coating a liquid containing the abovementioned organosilane or its hydrolyzed substance onto the dent and projection surface (that is, coating method), a method for immersing a dent and projection film formed article into a liquid containing the abovementioned organosilane or its hydrolyzed substance (that is, a liquid phase chemical adsorption method), a method for placing a dent and projection film formed article in steam of the abovementioned organosilane or its hydrolyzed substance and adsorbing the same there on (that is, gas phase chemical adsorption method) may be listed.
Of the abovementioned methods, the abovementioned coating method may depend upon an already known technique, and it is specially preferable. There are many methods which are a method of using a device such as a spin coater, roll coater, spray coater, curtain coater, etc., an immersing method (dip coating method), a flow-coating method, a method for rubbing the dent and projection surface with a cloth or paper impregnated with a coating liquid in a state where the cloth or paper is brought into contact with the surface (rubbing method), and various kinds of printing methods such as a screen printing, gravure printing, curved printing, etc.
Furthermore, although there is a case where the organosilane coating liquid is not uniformly coated by being shed depending on a dent and projection film coated on the matrix surface and including metal oxide fine particles, wherein metal oxides are the matrix thereof, this can be improved by washing the surface of the substrate or improving the quality thereof.
As a method of washing or improving the quality, many ways, that is, de-oiling washing by an organic solvent such as alcohol, acetone, hexane, etc., washing with alkali or acid, ultrasonic cleaning, irradiation of ultraviolet rays, ozone treatment with ultraviolet rays, plasma treatment, corona discharge treatment, heat treatment, etc. are available.
A solvent for dissolving the abovementioned organosilane is not specially limited. However, preferably, water, alcohol, ketone, etc. may be employed along or by combination thereof in view of safety, cost, and operation efficiency. Methanol, ethanol, propanol, butanol, etc. may be listed as alcohol, etc. Acetone, methylethyl ketone, diethyl ketone, etc. may be employed as ketone, etc.
The abovementioned organosilane may be hydrolyzed for use as necessary. Water and acid catalyst may be added to organosilane as necessary, wherein hydrolysis is carried out for a fixed period of time at a fixed temperature, and organosilane is diluted for use as necessary.
Although the conditions of hydrolysis of organosilane are not specially limited, it is preferable that the hydrolysis is carried out for three minutes to fifty hours in an range of temperature from 20.degree. C. to 60 .degree. C. In a case where the temperature is lower than 20.degree. C. or the time is less than 3 minutes, the promotion of hydrolysis is not sufficient. To the contrary, if the temperature is higher than 60.degree. C. and the time exceeds 50 hours, the effect of promotion of hydrolysis can not be enhanced, the service life of the coating liquid is shortened. Therefore, that is not preferable.
As the abovementioned acid catalyst, mineral acids such as hydrochloric acid, sulphuric acid, nitric acid, etc., and organic acids such as acetic acid, formate acid, citric acid, para-toluenesulfonic acid, etc. may be used. The quantity of addition of acid is not specially limited. However, it is good that the quantity of addition of acid is from 0.0001 to 2 (molar ratio) with respect to organosilane. If the quantity of addition of acid is less than 0.0001 (molar ratio), promotion of hydrolysis of organosilane is not sufficient, and if the same exceeds 2 (molar ratio), the effect of hydrolysis promotion is no more improved. The acid becomes excessive to be unfavorable.
Though the quantity of water added for the abovementioned hydrolysis is not specially limited, it is good that the quantity is 0.1 or more (molar ratio) with respect to organosilane. If the quantity is less than 0.1 (molar ratio), promotion of the hydrolysis of organosilane is not sufficient to be unfavorable.
On the other hand, as regards organosilane, the hydrolysis speed of which is fast like, for example, chlorosilane, sufficient hydrolysis can be carried out with only water adsorbed on the dent and projection surface of metal oxides, wherein there is a case where organosilane can be fixed on the surface by a dehydration condensation reaction. In this case, since an anti-fogging article which is superior in view of weathertightness, anti-fogging property and anti-fogging sustainability, can be obtained, it is preferable that a coating liquid is prepared by using a non-water oriented solvent with the dissolved water sufficiently decreased. As a non-water oriented solvent, n-hexane, cychlohexane, xylene, toluene, etc. may be listed.
Furthermore, the concentration of organosilane used for coating is not specially limited, organosilane of 0.001 through 5 percents by weight is preferably used. If the concentration is lower than 0.001 percents by weight, no sufficient promotion of anti-fogging sustainability of an anti-fogging article obtained can be recognized, and if the concentration exceeds 5 percents by weight, the anti-fogging property is not improved anymore. Therefore, that is not economical and is not preferable.
It is preferable that the dent and projection substrate on which organosilane solution is coated is dried or heat-treated at a temperature from 20 through 180.degree. C. for three minutes to three hours. By this treatment, combination of organosilane with metal oxides is strengthened to cause the durability and anti-fogging sustainability of an anti-fogging article to be improved. If the temperature is less than 20.degree. C. or the treatment time is shorter than three minutes, the abovementioned effect is not sufficient to be unfavorable. Since there is a case where organosilane is decomposed if the temperature is higher than 180.degree. C. That is also unfavorable. Furthermore, even though the treatment time exceeds three hours, no more effect can be expected. Therefore, that is also unfavorable in view of the productivity.
If organosilane forms a simplex molecular layer on the abovementioned dent and projection surface, the anti-fogging sustainability can be improved, and since the thickness of organosilane exceeds 10nm, the effect is not increased any more, a preferable thickness of the organosilane layer after heat treatment is from 0.3 through 10 nm. Even in a case where the thickness of organosilane layer is comparatively large, it is necessary that the thickness of organosilane layer is not greatly fluctuated on places, and it is necessary that dents and projections which are similar to those of the abovementioned dent and projection surface, that is, dents and projections having an arithmetical mean roughness (Ra) from 1.5 to 80 nm and an average interval (Sm) of the dents and projections from 4 to 300 nm, are formed on the outside surface of the organosilane layer.
If a layer of surface-active agent is further coated onto the dent and projection film (regardless of whether or not the layer includes the abovementioned surface-active agent or phosphate compound) including the abovementioned metal oxide fine particles and having metal oxides as its matrix, or onto a layer of organosilane (or its hydrolyzed substance) including the abovementioned functional group covered on the dent and projection film surface, it is possible to obtain anti-fogging articles, the anti-fogging property and anti-fogging sustainability of which are further improved.
The abovementioned layer of surface-active agent is able to reduce the surface tension of dew-condensed water drops, wherein slippage of water drops is improved, and an effect of the anti-fogging property is further increased. Furthermore, the abovementioned layer of surface-active agent wraps stain constituents up and takes a role of preventing the anti-fogging property from being lowered due to stains on the surface.
Since the abovementioned surface-active agent layer is hardly eliminated due to its physical properties of the surface dent and projection film (dent and projection film including metal oxide fine particles and having metal oxides as its matrix) which is the underground thereof, the anti-fogging effect brought by the surface-active agent can last longer than a case where the surface-active agent is coated on a usual smooth substrate surface not having any dent and projection. Furthermore, as regards articles provided with a layer of organosilane, etc. including the abovementioned functional groups on the abovementioned dent and projection film surface, the surface-active agent is hardly eliminated by virtue of mutual acting force among molecules between the abovementioned functional group and surface-active agent on the layer surface in addition to the abovementioned physical shape, wherein the anti-fogging effect can be further improved by the surface-active agent.
In a case where the thickness of the coated surface-active agent layer is comparatively small in the range described later, dents and projections having an arithmetical mean roughness (Ra) from 1.5 to 80 nm and a mean interval (Sm) of dents and projections from 4 to 30 nm are formed by influences of its underground surface on the surface (outside) of the surface-active agent, whereby a higher anti-fogging property can be produced by the dent and projection shape. If the thickness of the surface-active agent layer is comparatively large, dents and projections formed on the surface (outside) of the surface-active agent layer do not become larger than 1.5 nm in view of the arithmetical mean roughness (Ra) and do not become larger than 4 nm in view of the mean interval (Sm) of dents and projections, wherein although the layer surface of the surface-active agent is made smooth, the anti-fogging effect is brought by the surface-active agent itself. As the surface-active agent is gradually flown out through continued use to cause the thickness of the surface-active agent layer to be decreased, dents and projections are caused to appear on the surface, wherein a higher anti-fogging property can be maintained by its dent and projection shape.
Non-ionized or negative-ionized surface-active agent is favorably used to be coated on the abovementioned surface. Since positive-ionized or ampholytic surface-active agent has such a tendency where the surface-active agent is adsorbed onto the dent and projection surface consisting of metal oxides with the hydrophilic portion of positive ions oriented thereto, the hydrophobic portion of the surface-active agent is oriented to the air side. Resultantly, since the hydrophilicity on the surface of articles is liable to be lowered to cause the anti-fogging property to be decreased, the positive ionized or ampholytic surface-active agent is not preferable to use.
Furthermore, a surface-active agent having amine nitrogen or amide combination is liable to be adsorbed onto the dent and projection film composed of metal oxides via nitrogen atoms regardless of ion polarity, wherein the anti-fogging property is also lowered. Therefore, the surface-active agent is not preferable. Accordingly, a surface-active agent not containing any amine nitrogen or amide combinations in molecules is preferably used.
However, articles provided with a layer of organosilane including the abovementioned functional group on its surface, the adsorption tendency of the abovementioned surface-active agent is lowered, a positive-ionized or ampholytic surface-active agent and a surface-active agent containing amine nitrogen or amide combinations in molecules are also favorably used.
As a negative-ionized surface-active agent, sulfosuccinic acid ester salt like dialkyl sodium sulfosuccinate, alkylether sulfate, aikylether phosphate, alkylether carbonate are available, and ester salt of sulfate like sodium dodecylbenzene sulfonate, etc. is also available. Of them, dialkyl sodium sulfosuccinate, for example, dibutyl sodium sulfosuccinate, dihexyl sodium sulfosuccinate, or di-2-ethylhexyl sodium sulfosuccinate, etc. has a good anti-fogging preventing property and anti-fogging sustainability and is preferably used.
As a non-ionized surface-active agent, there are available, polyoxyethylene alkyl ether like polyoxyethylene nonyl phenyl ether, polyoxy ethylene stearyl ether; polyoxy ethylene acyl ester like polyoxy ethylene monostearate; polyoxy ethylene sorbitan acyl ester like polyoxy ethylene sorbitan monostearate; sorbitan ester like sorbitan laurate, etc.
A non-ionized surface-active agent which has a hydrophilicity/lipophilicity balance value (HLB) from 5 through 18 is preferable. If the HLB value is smaller than 5, the hydrophilicity is low, where sufficient anti-fogging property can not be obtained. On the other hand, if the HLB value is larger than 18, the solubility with water becomes too high to cause the surface-active agent to be easily eliminated from the surface due to dew condensation. Therefore, the sustainability of the anti-fogging effect is decreased to be unfavorable. The surface-active agent to be coated on the abovementioned surface may be used alone or with two or more kinds thereof mixed.
Though the thickness of the abovementioned surface-active agent after being coated is not specially limited, the thickness may be roughly from 0.2 to 100 nm. If the thickness of surface-active agent is thinner than 0.2 nm (simplex molecular layer), dews may be condensed at some places on the surface, wherein the anti-fogging property and anti-fogging sustainability resulting from the surface-active agent is not remarkably promoted to be unfavorable. On the contrary, if the thickness is larger than 100 nm, interference color may be obtained, resulting from the surface-active agent, wherein unevenness and imbalance can be recognized. That is also unfavorable. A more preferable thickness thereof is from 10 to 100 nm.
An already-known method may be used for coating a surface-active agent without any special limitation. However, there are many methods which are; a method of using a device such as a spin coater, roll coater, spray coater, curtain coater, etc.; an immersing method (dip coating method); a flow-coating method; a method for rubbing the dent and projection surface with a cloth or paper impregnated with a coating liquid in a state where the cloth or paper is brought into contact with the surface (rubbing method); and various kinds of printing methods such as a screen printing, gravure printing, curved printing, etc.
A solvent for dissolving the abovementioned surface-active agent for coating is not specially limited. However, preferably, water, alcohol, etc. may be employed along or by combination thereof in view of safety, cost, and operation efficiency. Methanol, ethanol, propanol, butanol, etc. may be listed as alcohol, etc.
Furthermore, although the concentration of surface-active agent used for coating is not specially limited, it is preferable that the concentration thereof is from 0.001 to 5 percents by weight. If the concentration is lower than 0.001 percents by weight, the thickness of the surface-active agent on an anti-fogging article obtained is too small to hardly recognize any improvement of the anti-fogging property and anti-fogging sustainability, and if the concentration is larger than 5 percents by weight, the anti-fogging property will not be improved any more. That is not preferable in view of economicality.
Furthermore, a surface-active agent may be coated onto the abovementioned anti-fogging article which is in use or after use, for the purpose of regaining a lowered anti-fogging property.